Fluid actuatable fan clutches are used in conjunction with internal combustion engines, and more particularly diesel engines, in heavy duty vehicles to provide a cooling action when the engine is in an overheated condition. Air or other fluid is supplied to the fan clutch to actuate it in response to a thermally actuatable air valve, such as the one described in U.S. Pat. No. 3,955,760.
One such fluid-operated clutch mechanism is described in U.S. Pat. No. 3,253,687 in which a friction facing material is attached to a sheave rotatably mounted on a shaft, a hub portion is mounted on said shaft adjacent said sheave, and the hub has an internal, annular piston which can be urged into contact with the friction facing by air or other fluid pressure. However, in devices of this type, the outward thrust created by the piston being urged into contact with the friction facing material places a large load on the bearings which can lead to early failure.
U.S. Pat. No. 3,762,517 discloses a fluid-operated fan clutch which employs internal dual pistons acting in opposite directions. However, this concept requires a fairly complicated mechanical device and also still retains an outwardly thrusting reaction during actuation of the device.
A fan clutch is described in a bulletin numbered 20-0612 of the Schwitzer division of Wallace-Murray Corporation, Box 80-B, Indianapolis, Ind. in which a drive disk is engaged with the hub of a fan clutch by a squeezing action between a piston located in the hub and a plate attached to the hub. However, in this device the piston, drive disk and back-up plate are located on the external circumference of the hub, and the back-up plate is connected to the hub on the outer circumference thereof, which said construction still provides a considerable thrusting leverage.
It is an object of the present invention, therefore, to provide a fluid actuatable fan clutch in which there are substantially no outwardly acting thrusting forces acting on the bearings.